The
effect of a Microgravity environment on autonomic cardiovascular control, energy
expenditure and muscle characteristics

read about the Research Team

The decision of Mark Shuttleworth
to travel to space has provided South Africa with a unique opportunity to
promote and share our unique scientific research and technology with the rest of
the world. The Exercise Science and Sports Medicine Department of the University
of Cape Town together with Body iQ have proposed a study entitled “The effect
of a microgravity environment on autonomic cardiovascular control, energy
expenditure and muscle characteristics”. The rationale, aims and methodology
of the study are discussed below.

Both heart rate and blood
pressure are controlled by the autonomic nervous system. This nervous system is
an unconscious, or “automatic” nervous system, which consists of 2 parts –
the parasympathetic nervous system and the sympathetic nervous system. These 2
systems have opposing roles and are activated according to the different needs
of the individual. The parasympathetic nervous system is activated during rest
and assists in energy restoration by means of the digestion and absorption of
food. This system also acts to decrease heart rate. The sympathetic nervous
system, on the other hand, prepares the body for an emergency and counteracts
the parasympathetic nervous system in order to maintain the required energy
supply. During any emotional or physical stress, adrenaline is released by the
sympathetic nervous system, which acts to increase heart rate and blood
pressure.

Accordingly, heart rate is
controlled by the balance between parasympathetic (PNS) and sympathetic nervous
system (SNS) activity. On a beat-to-beat basis, however, it has been observed
that heart rate is not constant and there are periodical fluctuations indicative
of the relative contributions of each of these 2 components of the autonomic
nervous system. There have been various methods employed in an attempt to
quantify the relative contributions of each of these systems. One of the most
commonly used methods is the frequency domain analysis of heart rate
variability. This method uses highly sophisticated techniques to determine
different frequencies of heart rate and from this analysis can identify which
nervous system is predominantly active during both rest and exercise.

There have been very few studies
conducted during space flights that have measured this component of physiology,
and those that have been done have yielded conflicting results. Therefore, the
first aim of this study will be to determine whether the relative contributions
of the parasympathetic and sympathetic nervous system remain the same in space
when compared to earth and in this way we hope to provide additional information
to the scientific literature to either support or refute the notion that heart
rate variability is different between the 2 conditions. Heart rate will be
measured using an on-board electrocardiograph (ECG), after which, the collected
heart rate data will be transmitted to earth, via satellite, where it will be
analysed and interpreted.

A second aim of the study will be
to provide Mark with a number of specifically designed exercises that he will be
able to do both before he leaves for space as well as while he is in space.
Previous research has shown that although there is no muscle damage that occurs
during space flight, predominantly because there is no gravity to load the
muscles, as soon as the astronauts arrive back to earth they experience muscle
pain and stiffness. This muscle pain is similar to that which we experience on
earth after participating in any unaccustomed or strenuous exercise, and is
caused by miniature tears to the muscle fibres. This pain usually occurs a
little while after the exercise, and hence it has been referred to as delayed
onset muscle soreness (DOMS). Other studies have shown that if an exercise
causes this kind of response, it is likely that there may be some protective
effect on that muscle and that if the same exercise is performed on a second
occasion, this pain and muscle damage may be slightly less.

A component of space travel that
has been extensively studied is that of energy balance and energy expenditure.
The use of the doubly labeled water technique, a very accurate means of
measuring total daily energy expenditure (TEE), has previously been validated in
space with highly accurate results. It has been found that astronauts lose a
significant amount of body weight during space flight. This is attributed to the
maintenance of energy expenditure while dietary intake is significantly reduced,
resulting in a negative energy balance.

Another method for measuring TEE
is the heart rate monitoring (HRM) method. Heart rate monitors provide
relatively inexpensive, non-invasive tools that allow for the accurate
measurement of energy expenditure, provided the person has been individually
calibrated so that they have created their own heart rate-energy expenditure
curve. If HRM is proved to be an accurate measure of TEE, when compared to the
doubly labeled water technique, in micro-gravity, then this should strengthen
the accuracy of this method on Earth and further encourage the use of this
relatively inexpensive method amongst Africans in group based population
studies.

The practical importance of these
different studies has direct relevance to South Africa and to South African
technology. Our previous and current research of health and fitness parameters
in the general South African public has illustrated a need for scientific
communication and expertise outside of the boundaries of our building.
Accordingly, we have aimed to develop technology that will enable South African
scientists to evaluate both athletes and the general public at a distance and to
provide them with new and relevant information specific to their sport and well
being. By studying Mark Shuttleworth in Russia and aboard the ISS, we will begin
both to demonstrate and develop the capacity for this distance coaching and
evaluation, using data such as heart rate. We believe that this experience will
provide the necessary impetus and opportunity to develop the capacity for
distance coaching and evaluation, throughout South Africa and, in due course,
the rest of the world.

South Africa has one of the
highest recorded incidences of chronic diseases of lifestyle, which include
heart disease, hypertension, diabetes and obesity. The fundamental underlying
factor contributing to most of these diseases has been shown to be physical
inactivity, as expressed by total daily energy expenditure. Heart rate and blood
pressure are both practical measurements of health that the South African, and
international, public are able to relate to. This research project aims to
promote the understanding and importance of these variables and how they are
affected during physical activity. Both heart rate and blood pressure will be
broadcast via the Internet to a South African based web site, driven by Body iQ.
This company, who have developed a novel methodology both designed and
engineered in South Africa to measure and promote health, will analyse and
interpret the information that is received directly from Mark in space. This
will be a world first. As a result, the exposure of Mark’s heart rate, blood
pressure and total daily energy expenditure variables to the public will create
maximal awareness of health, as well as aiding in the promotion of the use of
physical activity in the improvement of health in South Africa.

Ultimately, the international
exposure of South African science may interest international funding sources and
collaborative relationships. This will further strengthen our investigative
capabilities as well as our standing in international research.